This invention pertains to an improved type of mobile telephone system, in general, and to an improved cellular mobile radio telephone system, in particular.
Cellular Mobile Radio Service (CMRS) is a fully automatic radiotelephone service for use by mobile, portable, or stationary units specifically designed with sophisticated digital controls and logic. The radiotelephone units utilize radio frequency to communicate with low power, limited radiation base transceivers in a cellular pattern making it necessary for the system to locate each mobile unit and follow it enroute by "handing off" in-progress calls between cells. The low power, limited radiation elements of CMRS systems allow a unique frequency distribution and reuse scheme to provide sufficient channels to serve any number of subscribers (i.e. 100,000).
The mobile radios are intelligent units; that is, they contain a microprocessor equivalent logic element. They store certain permanent information (i.e. unit manufacturer's serial number), semi-permanent information (i.e. registration memory), temporary memory containing individual call data and timers, etc. In the United States, as a result of FCC regulations, each unit can access 666 radio channels but must manually or automatically select either an upper band of 333 or a lower band. (Current FCC rules allocate the upper band to a non-wire line RCC and the lower band to a telco owned RCC).
The base radio "stations" are located in a pattern of "cells" of from about 1 mile to up to 10 miles across which form a patchwork coverage of the desired area. Each cell radio operates with several assigned channels selected so that they do not interfere with channels of nearby cells. Due to the restricted power and range of cell radio transmitters, each set of cell frequencies may be reused in a cell only a few miles away.
One CMRS system called the "Advanced Mobile Phone Service" (AMPS) system is described in great detail in "The Bell System Technical Journal," January, 1979, Vol. 58, No. 1, pages 1-269. In the AMPS system control of the various transceivers at a cell site is via dedicated wires to a central processor.